[Angular] Difference between Service, Factory and Provider in AngularJS

gistfile1.txt

var myApp = angular.module('myApp', []);
 
//service style, probably the simplest one
myApp.service('helloWorldFromService', function() {
    this.sayHello = function() {
        return "Hello, World!"
    };
});
 
//factory style, more involved but more sophisticated
myApp.factory('helloWorldFromFactory', function() {
    return {
        sayHello: function() {
            return "Hello, World!"
        }
    };
});

//provider style, full blown, configurable version    
myApp.provider('helloWorld', function() {
    // In the provider function, you cannot inject any
    // service or factory. This can only be done at the
    // "$get" method.

    var name = 'Default';

    return {
        $get: function() {
            return {
                sayHello: function() {
                    return "Hello, " + name + "!"
                }
            }
        },
        setName: function(newName) {
            name = newName;
        }
    };

});